(i) Field of the Invention
The present invention relates to an aqueous ink composition for ball point pens.
(ii) Description of the Related Art
In an aqueous ink composition for ball point pens, a water-soluble high-boiling organic solvent such as a polyvalent alcohol, for example, glycol or glycerin has been used as a dry inhibitor in addition to water. When the aqueous ink containing such an organic solvent is used for writing, frictional resistance between a tip ball and a ball holder in a pen point increases by the rotation of the ball. In consequence, at the time of the writing, a ball receiver is noticeably worn, so that a writing performance deteriorates and the flow of the ink through the pen point becomes inconveniently nonuniform owing to the deterioration of the tip. For the purpose of overcoming such a drawback, it has been attempted to add a lubricity improver. Japanese Patent Publication No. (Sho) 62-58394 has disclosed an ink to which an unsaturated fatty acid or a water-soluble cutting agent is added as a lubricant.
However, even if the above-mentioned ink additive is added to the ink in accordance with the conventional technique, the lubricating properties are not sufficient, and an unwritable phenomenon occurs owing to the wear of the ball receiver. Even though the sufficient lubricating properties can be obtained, there is a practical problem that the surface tension of the ink noticeably deteriorates, with the result that the feathering of written lines tends to occur.